Ultraviolet (UV) radiations of sunlight ranging from 280 to 400 nm are known to exert a damaging action on organic materials, such as plastics and paints, which are destroyed more or less rapidly. Destruction is apparent in the form of yellowing, discolouration, brittlening and generally as a loss of mechanical properties of the organic material.
It is known as well that UV radiations, particularly the so called UV-B between 290 and 320 nm, are noxious to human skin. They cause skin erythema and sunburns, whose severity depend on duration of exposure. It was ascertained that also radiations between 320 and 400 nm, so called UV-A, responsible of skin suntan, can cause alterations and damages to the skin which can not be disregarded, particularly in the case of sensitive skins or of continued exposure to sunlight. It has ben demonstrated that UV-A radiation, other than damaging elastine and collagen, can also be the cause of a number of phototoxic or photoallergic reactions. Moreover, the noxious action of UV-B radiation may be enhanced by the presence of UV-A. (Willis et al.; Journal of Investigative Dermatology, vol. 59,416, 1072).
For the protection against noxious UV-B radiations, some compounds, such as for example cinnamic acid, 4-aminobenzoic acid, benzylydenecamphor and benzophenone derivatives, are well-known and also used for the preparation of cosmetic compositions.
On the contrary, for the protection against UV-A, products with sufficient efficacy are not yet available, even if patent literature provides different compounds, but in practice the result is not satisfying.
2-hydroxy-4-methoxybenzophenone is a commercially available product, whose maximum absorption about 325 nm is too low in order to provide a sufficient protection, moreover its solubility in the solvents generally used in cosmetics is very low and this makes its use difficult. Another compound presently used in practice is a dibenzoylmethane derivative, but this compound has not sufficient photostability (Int.J.Cosm. Science, 10, 53, 1988).
Accordingly the sunscreen cosmetic compositions containing the above compounds can not assure a sufficient protection against UV-A, because the active ingredients are either too weak (benzophenone derivatives) or are degraded too fast from the sun radiation itself (dibenzoylmethane derivative).
To date, also for the stabilization of synthetic polymers and paints, industry has no products with sufficient efficacy and with characteristics suitable to provide a satisfactory protection against the damaging action of UV radiations.
Compounds similar to the ones of formula (I) below are disclosed in U.S. Pat. No. 3079366, DE 4122475 and DE 4211603, but their use is not completely satisfying.
Therefore the need to have photostabilizing agents and sunscreens for cosmetics satisfying the above requirements, such as solubility in cosmetic vehicles, effective absorption of UV radiation, particularly sunlight, time-stability, is still present.